Camptothecin (CPT) is an alkaloid contained in leaves and bark of Camptotheca Acuminata (Chinese origin) and other plants. Irinotecan (7-ethyl-10-[4-(1-piperidino)-1-piperidino]carboxyoxycamptothecin) hydrochloride (CPT-11) (Patent Document 1), which is a semi-synthetic derivative of camptothecin, is a particularly important substance, since the irinotecan maintains a high anti-tumor activity originating from camptothecin and exhibits reduced toxicity. CPT-11 is known to be metabolized in the body into 7-ethyl-10-hydroxycamptothecin (SN-38) (Patent Document 2), which is a semi-synthetic derivative thereby exhibits the relevant activity.
Generally, camptothecins such as CPT-11 are intravenously administered to patients in need thereof. Therefore, these compounds are commercialized as injections which have been adjusted to become isotonic by use of an agent such as sorbitol, and are employed in practice. Various attempts have been made to formulate the camptothecins into different preparations. For examples there have been known a controlled-release drug containing a camptothecin derivative incorporated into collagen-2-hydroxyethyl methacrylate copolymer (Patent Document 3) and a controlled-release drug containing a camptothecin or a derivative thereof carried by poly(lactic acid-glycolic acid) copolymer (Patent Document 4).
However, since CPT-11 has poor solubility in water, an aqueous drug product thereof needs to be prepared through heating which is not preferred. Therefore, there is demand for development of a novel irinotecan derivative which has high water solubility and which enables production of aqueous drug products without heating, for the purpose of simplifying the drug production steps.    Patent Document 1. JP-B-1991-4077    Patent Document 2: JP-B-1987-47193    Patent Document 3: JP-A-1995-277981    Patent Document 4: JP-A-1998-17472